Status of the Project on April, 2012

Objective of the project is to design a geodetic instrument for determination of vertical deflections - value and direction of horizontal component of local gravity field. Gravimeters allow only gravity field module determination, to directly determine deflections, accurate measurement of difference between gravity field (plumb line) and geodetic vertical directions is needed. Recent success in a number of scientific and technological fields has made this task real:

- Accurate and representative astrometric star catalogs,

- Development of CCD technology, providing unprecedent sensitivity, accuracy and ease of automated usage of astrometric imaging devices,

- Achievements in high accuracy tiltmeter technology, allowing fast, accurate and easy determination of plumb line direction.

Zenith cameras for this kind of measurements have been designed and are being designed by some research groups, yet their number and accessibility is still small. Our goal is make a portable, cheap and robust instrument, using standard components and ensuring necessary properties by sophisticated data processing algorithms.

The first half of project is over. During this time we have assembled a prototype zenith camera, all principal hardware components are integrated in it and working.

The basic algorithms for control and data processing software have been developed and tested and are working properly. They include reference star catalog database management, modules for star apparent position and zenith position calculations, high precision tiltmeter control and data acquisition module. A number of observation sessions are demonstrated, that instrument so far functions according to planned properties. Analysis of observation data led to improvements in instrument geometry model, algorithm for model parameter calculation was developed and first real vertical deflection estimations were calculated. Still, improvements in star image acquisition time moment accuracy and automation of instrument positioning and data acquisition are needed to achieve planned functionality and accuracy.

Presently zenith camera assembly is being modified to add CCD centering mechanism and stepper motor block for positioning of instrument compartment.

Besides,  in order to support interpretation of observation results and select optimal locations for measurements, data collection and evaluation on Baltic region geoid and research concerning potential use of vertical deflection data together with gravimetric measurements are being done, including processing GNSS data from LATPOS and EUPOS-Riga networks using Bernese software package.